Apparatus and Method for Memory Address Encryption

ABSTRACT

An apparatus for encrypting an input memory address to obtain an encrypted memory address comprises an input interface for receiving the input memory address being an address of a memory. Moreover, the apparatus comprises an encryption module for encrypting the input memory address depending on a cryptographic key to obtain the encrypted memory address. The encryption module is configured to encrypt the input memory address by applying a map mapping the input memory address to the encrypted memory address, wherein the encryption module is configured to apply the map by conducting a multiplication and a modulo operation using the cryptographic key and a divisor of the modulo operation, such that the map is bijective.

TECHNICAL FIELD

The present invention relates to encryption, and, in particular, to anapparatus and method for memory address encryption.

BACKGROUND

Memory and address encryption become more and more important.

On a controller in a smartcard or similar security device theimplementation of memory encryption and in particular address encryptionis subject to severe and timing constraints.

It would be highly beneficial if improved concepts for memory andaddress encryption would be provided.

SUMMARY

According to an embodiment, an apparatus for encrypting an input memoryaddress to obtain an encrypted memory address is provided. The apparatuscomprises an input interface for receiving the input memory addressbeing an address of a memory. Moreover, the apparatus comprises anencryption module for encrypting the input memory address depending on acryptographic key to obtain the encrypted memory address. The encryptionmodule is configured to encrypt the input memory address by applying amap mapping the input memory address to the encrypted memory address,wherein the encryption module is configured to apply the map byconducting a multiplication and a modulo operation using thecryptographic key and a divisor of the modulo operation, such that themap is bijective.

According to another embodiment, an apparatus for encrypting an inputmemory address to obtain an encrypted memory address is provided. Theapparatus comprises an input interface for receiving the input memoryaddress being an address of a memory. Moreover, the apparatus comprisesa segmentation module for segmenting the input memory address into aplurality of input memory address segments. Furthermore, the apparatuscomprises an encryption module for encrypting each input memory addresssegment of the plurality of input memory address segments depending onone of a plurality of cryptographic subkeys. The encryption module isconfigured to encrypt said input memory address segment by applying amap mapping said input memory address segment to an encrypted memoryaddress segment, said encrypted memory address segment being one of aplurality of encrypted memory address segments, wherein the encryptionmodule is configured to apply the map by conducting a multiplication anda modulo operation using one of the plurality of cryptographic subkeysand one of a plurality of divisors, such that the map is bijective. Theencrypted memory address segments of the plurality of encrypted memoryaddress segments together form the encrypted memory address.

According to a further embodiment, an apparatus comprising a memory, aCPU for processing data being stored at memory addresses in the memory,and an address encryption unit for encrypting an input memory address ofthe memory to obtain an encrypted memory address is provided. Theaddress encryption unit comprises an input interface for receiving theinput memory address, and an encryption module for encrypting the inputmemory address depending on a cryptographic key to obtain the encryptedmemory address. The encryption module is configured to encrypt the inputmemory address by applying a map mapping the input memory address to theencrypted memory address. The encryption module is configured to applythe map by conducting a multiplication and a modulo operation using thecryptographic key and a divisor of the modulo operation, such that themap is bijective.

Moreover, The apparatus of a further embodiment is provided. Theapparatus comprises a CPU for providing an original logical address, anMMU for generating a shifted logical address depending on the originallogical address, an address encryption unit for encrypting the shiftedlogical address to obtain a physical address, the address encryptionunit comprising an input interface for receiving the shifted logicaladdress, and further comprising an encryption module for encrypting theshifted logical address depending on a cryptographic key to obtain thephysical address, wherein the encryption module is configured to encryptthe shifted logical address by applying a map mapping the shiftedlogical address to the physical address, wherein the encryption moduleis configured to apply the map by conducting a multiplication and amodulo operation using the cryptographic key and a divisor of the modulooperation, such that the map is bijective, a data encryption-decryptionunit for encrypting first plaintext data to obtain first ciphertext dataand for decrypting second ciphertext data to obtain second plaintextdata, a key storage for storing the cryptographic key, and a memorybeing configured to either store the first ciphertext data at thephysical address, or to provide the second ciphertext data being storedat the physical address to the data encryption-decryption module.

According to another embodiment, a method for encrypting an input memoryaddress to obtain an encrypted memory address is provided. The methodcomprises:

-   -   Receiving the input memory address being an address of a memory,        and:    -   Encrypting the input memory address depending on a cryptographic        key to obtain the encrypted memory address.

Encrypting the input memory address comprises applying a map mapping theinput memory address to the encrypted memory address by conducting amultiplication and a modulo operation using the cryptographic key and adivisor of the modulo operation, such that the map is bijective.

According to a further embodiment, a method for encrypting an inputmemory address to obtain an encrypted memory address is provided. Themethod comprises:

-   -   Receiving the input memory address being an address of a memory.    -   Segmenting the input memory address into a plurality of input        memory address segments, and    -   Encrypting each input memory address segment of the plurality of        input memory address segments depending on one of a plurality of        cryptographic subkeys to obtain the encrypted memory address,        wherein encrypting said input memory address segment comprises        applying a map mapping said input memory address segment to an        encrypted memory address segment of a plurality of encrypted        memory address segments by conducting multiplication and a        modulo operation using one of the plurality of cryptographic        subkeys and one of a plurality of divisors, such that the map is        bijective.

The encrypted memory address segments of the plurality of encryptedmemory address segments together form the encrypted memory address.

Before embodiments of the present invention are described in detailusing the accompanying figures, it is to be pointed out that the same orfunctionally equal elements are given the same reference numbers in thefigures and that a repeated description for elements provided with thesane reference numbers is omitted. Hence, descriptions provided forelements having the same reference numbers are mutually exchangeable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an apparatus for encrypting an input memory addressto obtain an encrypted memory address according to an embodiment,

FIG. 2 illustrates an encryption module 120 according to an embodiment,

FIG. 3 illustrates an apparatus for encrypting an input memory addressto obtain an encrypted memory address according to an embodiment,

FIG. 4 illustrates an apparatus comprising a memory 410, a CPU 420 andan address encryption unit 430 according to an embodiment,

FIG. 5 illustrates an approach for address encryption,

FIG. 6 illustrates another approach for address encryption,

FIG. 7 illustrates a further approach for address encryption,

FIG. 8 illustrates The apparatus of a further embodiment, comprising aCPU, an MMU, an address encryption unit, a data encryption-decryptionunit, a key storage and a memory, and

FIG. 9 illustrates the effect of combined data encryption and addressencryption.

DETAILED DESCRIPTION

Before describing preferred embodiments in detail, some reasoning onaddress encryption is provided which helps to provide a betterunderstanding of the preferred embodiments.

Address encryption may be realized as a bijective map f, e.g. apermutation from plain addresses a to encrypted addresses a′. Themapping is controlled by a key k:

a′=f _(k)(a).

For test purposes, such as production tests, it may be important to havea keyed function a′=f_(k)(a), for which there is an identity-key, calledk₀, with the property that it yields the identity map, i.e. a=f_(k0)(a).This means scrambling is switched off.

The implementation of such a function may be critical in microcontrollerarchitecture, because of several reasons. For example, any delay in theaddress path from the controller to the memory (see figure: path fromMMU to memory) leads to deterioration of the system performance. If theimplementation needs a large number of gate delays, additional clockcycles for the memory access are needed. Moreover, complex designs leadto high power consumption, because memory addressing is highly frequent.

It may often be sufficient that the address encryption is notcryptographically hard, but that sufficient scrambling is provided tomake subsequent attacks harder. For example, address scrambling makesthe identification of data blocks, necessary for a cryptanalysis of thememory encryption of data, much more difficult. Secondly, addressscrambling renders the identification of memory blocks for subsequentfault injection attacks much more difficult.

Address encryption may be realized by a first approach as illustrated byFIG. 5, where an exclusive-OR of the addresses with a key is conducted:

f _(k)(a)=a⊕k.

Advantages of this approach are a minimal gate count, a minimumperformance impact, because of minimal circuit depth (only 1 gate delayis added), and an existence of an identity key: For k=0 scrambling isdisabled. However, such an approach realizes only a linear map, e.g.such an approach has no cryptographic strength at all. The approachworks on a bit-by-bit basis, and i.e. there is no mixing of bits. Hence,it can be re-engineered and broken easily. This results in low-endsecurity.

Modifying the approach of FIG. 5, a related simple scrambling may be itpie enter

Alternatively, address encryption may be realized by a second approach,as illustrated by FIG. 6, where a block cipher BC is used forencryption:

f _(k)(a)=BC(key=k,a).

An advantage of such an approach is high cryptographic strength, if astrong cipher is used. Disadvantages are a high gate count, a drasticperformance degradation, because block ciphers are round based, andcryptographically hard block ciphers need a high round number, e.g. 16for DES or 10 for AES-128. Hence, the critical access time to memory isincreased by a huge factor, as several additional clock cycles areneeded in the address phase, and there is usually no (known)identity-key. The identity map must be realized by an additional bypassusing multiplexors.

The approach illustrated by FIG. 6 may be implemented with a stronglyreduced round number, e.g. only 1 or 2 rounds. In this case thecryptographic strength is almost completely lost. Hence, the investmentof high hardware costs does not pay off at all.

Alternatively, address encryption may be realized by a third approach,as illustrated by FIG. 7, where a set of substitution boxes (S-boxes) isused. Assuming

S(a)=(S ₁(a ₁),S ₂(a ₂), . . . S _(n)(a _(j)))

is a set of j m-to-m S-boxes, each of which maps a disjoint subrange ofthe address space. Then, assuming

f _(k)(a)=S(a)⊕k

or

f _(k)(a)=L(S(a),k)

with L some linear operation.

This corresponds basically to one round of a classical block cipher (seeb) with one S-box layer, a key addition step, and optionally some lineardiffusion layer.

An advantage of this approach is that it can he constructed such that anidentity key exists. However, disadvantages are that even small S-boxeslike 4×4 S-boxes already have a high gate count and a high circuitdepth. They contribute usually with a significant number of gate delayswhich deteriorates the performance of the memory access. As aconsequence, an extra clock cycle may be needed in the address phase.Moreover, such an approach has only medium cryptographic strength. Theapproach illustrated by FIG. 7 lacks cryptographic strength, and adeterioration of the memory access time similar to the second approachaccording to FIG. 6 results.

Preferred embodiments avoid the disadvantages of the approachesillustrated by FIGS. 5, 6 and 7.

FIG. 1 illustrates are apparatus for encrypting an input memory addressto obtain an encrypted memory address according to an embodiment.

The apparatus comprises an input interface 110 for receiving the inputmemory address being an address of a memory.

Moreover, the apparatus comprises an encryption module 120 forencrypting the input memory address depending on a cryptographic key 121to obtain the encrypted memory address.

The encryption module 120 is configured to encrypt the input memoryaddress by applying a map mapping the input memory address to theencrypted memory address.

The encryption module 120 is configured to apply the map by conducting amultiplication and a modulo operation using the cryptographic key 121and a divisor 122 of the modulo operation, such that the map isbijective.

According to an embodiment, the input memory address, the encryptedmemory address, the cryptographic key 121 and the divisor 122 of themodulo operation may each indicate a polynomial. In such an embodiment,the divisor 122 may indicate a polynomial which is an irreduciblepolynomial.

In some embodiments, the divisor 122 may indicate a polynomial, which isan irreducible polynomial, where all coefficients of the irreduciblepolynomial are rational. Regarding polynomials where all are rational, apolynomial may, for example, be considered as being irreducible, if itcannot be expressed as the product of two or more polynomials where allcoefficients are rational, such that each of said two or morepolynomials where all coefficients are rational has a lower degree thanthe original polynomial.

However, in some embodiments, the divisor 122 may indicate a polynomialwhich is an irreducible polynomial, and wherein one, some or allcoefficients of the irreducible polynomial are not rational.

FIG. 2 illustrates an encryption module 120 according to a particularembodiment, where the encryption module 120 is configured to apply themap by employing the formula:

a′=ak(mod p)

In such an embodiment, a indicates the input memory address, a′indicates the encrypted memory address, k indicates the encryption key,and p indicates the divisor.

E.g., as a simplified example, consider that:

a=1001; k=1101; p=101

Then, the hits of the hit-sequence may represent coefficients of apolynomial over the Galois field GF(2):

polynomial (a)=1˜x³+0·x ²+0·x ¹+1·x ⁰ =x ³+1

polynomial(k)=1·x ³+1·x ²+0·x ¹+1·x ⁰ =x ³ +x ²+1

polynomial(p)=1·x ²+0·x ¹+1·x ⁰ =x ²+1

Here, x²+1 is an irreducible polynomial over GF(2).

In contrast, a polynomial x² is a reducible polynomial, as x²=x·x.

For example, some embodiments may apply the general rule that a hitsequence:

b _(n−1) b _(n−2) b _(n−3) . . . b ₂ b ₁ b ₀

indicates the polynomial:

b _(n−1) x ^(n−1) +b _(n−2) x ^(n−2) +b _(n−3) x ⁻³ + . . . +b ₂ x ² +b₁ x+b ₀.

Moreover, it should be noted that according to embodiments, for example,

a k (mod p)

means

(a k) mid p;

(e.g. at first: multiplication of a and k; then modulo division of theresult by

According to a particular embodiment, the address a and the key k areconsidered as elements of a polynomial ring, e.g. the extension fieldF_(q)[x]/(p), with p being some irreducible polynominal.

In a particular embodiment, the characteristic q=2 is chosen, so thataddress bit ranges can be assigned to field elements.

Then the address encryption can be written as a modular multiplication:

a′=ak(mod p)

According to other embodiments, an auxiliary key h is employed suchthat:

a′=ak(mod p)+b

Here “+” denotes the addition in the field, e.g., exclusive-Or (⊕) forq=2.

For a fixed, e.g. preselected, value of k≠0 and p being irreducible, themap is bijective and generates a permutation of the set of originaladdress values. Because of this property, the polynomial ring operationcan be used as an address encryption.

Compared with prior art, embodiments for efficient address scrambling asprovided here are particularly advantageous.

For example, generally, the field multiplication can be implemented suchthat it is performed with only a few gate delays. That means it can bedone one-the-fly within the address clock cycle (no additional clockcycle needed). For sparse polynomials p the gate delay of the circuit isvery small.

Moreover, area and power consumption are smaller compared to prior artsolutions.

Furthermore, security is improved compared to the “X or” prior artapproach described above and comparable to “S-Box layer” prior artapproach described above, but at significantly reduced area and powercosts. A well-chosen polynomial will generate a highly nonlinear mixingof the address bits.

Moreover, according to embodiments, a natural identity-key k=1 mightexist, which is useful for production test purposes. So, according tosome embodiments, the apparatus is configurable to select an identitykey as the encryption key k, such that

ak(mod p)=a mod p.

Furthermore, according to embodiments, a zero key, which yields a′=0.This can be used as a security countermeasure: If an attack is detectedthe key can be cleared to all−0. In this case all access will be mappedto address 0 (or a fixed address b, if the affine variant is employed).It is advantageous that this address contains only dummy data, such theattacker will only read dummy data from then on. Thus, according to someembodiments, the apparatus is configurable to select a zero key as theencryption key k, such that

ak(mod p)=0.

According to some embodiments which the encryption module 120 isconfigured to apply the map by employing the formula

a′=ak(mod p)+b,

wherein a indicates the input memory address, wherein a′ indicates theencrypted memory address, wherein k indicates the encryption key,wherein p indicates the divisor, and wherein b indicates an auxiliarykey.

In some embodiments, the apparatus is configurable to select an identitykey as the encryption key k, such that

ak(mod p)+b=a mod p+b.

According to some embodiments, the apparatus is configurable to select azero key as the encryption key k, such that a k (mod p)+b=b.

Some embodiments provide versions of the above-described concepts withsegmented address ranges. The presented address scrambling method canalso be applied to segmented address spaces. An address granularity maybe introduced by the controller's memory hierarchy. For example, anon-volatile memory contains a number of N_(s) segments (which can beerased at a time). each of which contains a number of N_(b) blocks(which are programmed at a time), each of which contains a number ofN_(w) words (determined by the processor word width), each of whichcontains a number of N_(b) bytes. When applying scrambling, it is inpractice only possible to exchange a data unit with another data unitwithin the same parent unit. For example, only blocks in the samesegment may be exchanged, only words in the same block may be exchanged,and so forth.

Accordingly, FIG. 3 illustrates an apparatus for encrypting an inputmemory address to obtain an encrypted memory address according toanother embodiment.

The apparatus comprises an input interface 310 for receiving the inputmemory address being an address of a memory.

Moreover, the apparatus comprises a segmentation module 315 forsegmenting the input memory address into a plurality of input memoryaddress segments.

Furthermore, the apparatus comprises an encryption module 320 forencrypting each input memory address segment of the plurality of inputmemory address segments depending on a respective one of a plurality ofcryptographic subkeys. The encryption module 320 is configured toencrypt said input memory address segment by applying a map mapping saidinput memory address segment to an encrypted memory address segment,said encrypted memory address segment being one of a plurality ofencrypted memory address segments. The encryption module 320 isconfigured to apply the map by conducting a multiplication and a modulooperation using one of the plurality of cryptographic subkeys and one ofa plurality of divisors, such that the map is bijective.

The encrypted memory address segments of the plurality of encryptedmemory address segments together form the encrypted memory address.

In an embodiment, each of the plurality of input memory address segmentsindicates a polynomial of a first group of polynomials, wherein each ofthe plurality of encrypted memory address segments indicates apolynomial of a second group of polynomials, wherein each of theplurality of cryptographic subkeys indicates a third polynomial, andwherein each of the pier f divisors indicates a fourth polynomial beingan irreducible polynomial.

According to an embodiment, the encryption module 320 is configured toencrypt each of the input memory address segments by applying said mapmapping said input memory address segment to one of the plurality ofencrypted memory address segments, by employing the formula

a _(i) ′=a _(i) k _(i)(mod p _(i)),

wherein i indicates an index of said input memory address segment,wherein a_(i) indicates said input memory address segment, whereina_(i)′ indicates one of the plurality of encrypted memory addresssegments, wherein k_(i) indicates one of the encryption subkeys, andwherein p_(i) indicates one of the divisors.

In a particular embodiment the (input) address is split into segmentsa=(a₁, a₂, . . . , a_(n)), for example, according to the memoryhierarchy of the system, subkeys k₁, k₂, . . . , k_(a) are derived froma key k. For example, a subkey derivation could be a segmentation of thekey into bit ranges k=(k₁, k₂, . . . , k_(n)). Different reductionpolynomials p₁, p₂, . . . , p_(n) may be used. Then the map of thescrambling operation of the total memory system may, for example, beachieved by

a₁’ = a₁k₁(mod  p₁)a₂’ = a₂k₂(mod  p₂)⋯a_(n)’ = a_(n)k_(n)(mod  p_(n)).

As the operations on all hierarchy levels can be done in parallel, thereis no additional penalty for the performance.

According to an embodiment, the apparatus is configurable to select foreach input memory address segment a_(i) of the input memory addresssegments an identity key as the encryption key k_(i), such that a_(i)k_(i) (mod p_(i))=a_(i) (mod p_(i)).

In an embodiment, the apparatus is configurable to select for each inputmemory address segment a_(i) of the input memory address segments a zerokey as the encryption key k_(i), such that a_(i) k_(i) (mod p_(i))=0.

According to an embodiment, the encryption module 320 is configured toencrypt each of the input memory address segments by applying said mapmapping said input memory address segment one of the plurality, ofencrypted memory address segments, by employing the formula

a _(i) ′=a _(i) k _(i)(mod p _(i))+b _(i).

wherein i indicates an index of said input memory address segment,wherein a_(i) indicates said input memory address segment, whereina_(i)′ indicates said one of the plurality of encrypted memory addresssegments, wherein k_(i) indicates one of the encryption subkeys, whereinp_(i) indicates one of the divisors, and wherein b_(i) indicates one ofa plurality of auxiliary keys.

In an embodiment, the apparatus is configurable to select for each inputmemory address segment a_(i) of the input memory address segments anidentity key as the encryption k k_(i), such that

a _(i) k _(i)(mod p _(i))+b _(i) =a _(i) (mod p _(i))+b _(i).

According to an embodiment, the apparatus is configurable to select foreach input memory address segment a_(i) of the input memory addresssegments a zero key as the encryption key k_(i), such that

a _(i) k _(i)(mod p_(i))+b _(i) =b _(i).

In particular embodiments, further diversification or scrambling of theencrypted memory address segments is provided by using, for the mappingof an input memory address segment a_(i) to an encrypted memory addresssegment a_(i)′, one or more bits from of the input memory address otherthan bits of the input memory address being mapped. In other words, allor part of one or more other input memory address segments may beincorporated into the mapping. Thus, for example, the encryption modulemay be configured to conduct, for each of one or more of the inputmemory address segments, a multiplication and modulo operation asdescribed above, but using one or more bits of the input memory addressother than bits of the input memory address segment being mapped. Thismay he done in any of several different ways. For example, one or morebits of the input memory address may be incorporated into or used tomodify or select the cryptographic subkey k_(i), in some embodiments, orincorporated into or used to modify or select an auxiliary key b_(i), inothers, or some combination of both, in still others. In any of these orin embodiments, one or more of the input memory address bits may beincorporated into or used to modify or select the divisor p_(i).

It will be appreciated that these approaches, in which input memoryaddress bits from portions of the input memory address other the inputmemory address segment being encrypted are incorporated into themapping, will diversify the output from the mapping, so that the sameinput memory address segment will map to different encrypted memoryaddress segments, depending on those other bits. This will make it moredifficult for an attacker to identify blocks of encrypted memoryaddresses that belong together, since, for example, an input memoryaddress segment that contains high-order bits of the input memoryaddress, which will change only occasionally as the range of memoryaddresses is scanned in order, will map to very different encryptedmemory address segments, in dependence on the lower-order bits of theinput memory address.

FIG. 4 illustrates an apparatus 400 comprising a memory 410, a CPU 420for processing data being stored at memory addresses in the memory, andan address encryption unit 430 for encrypting an input memory address ofthe memory to obtain an encrypted memory address according to anembodiment.

The address encryption unit 430 comprises an input interface 431 forreceiving the input memory address, and an encryption module 432 forencrypting the input memory address depending on a cryptographic key toobtain the encrypted memory address.

The encryption module 432 is configured to encrypt the input memoryaddress by applying a map mapping the input memory address to theencrypted memory address. Moreover, the encryption module 432 isconfigured to apply the map by conducting a multiplication and a modulooperation using the cryptographic key and a divisor of the modulooperation, such that the map is bijective.

In some embodiments, the address encryption unit 430 may be an apparatusfor encrypting an input memory address to obtain an encrypted memoryaddress according to one of the above-described embodiments.

FIG. 8 illustrates an architecture where address encryption, e.g.address encryption according to one of the above-described embodiments,may he employed.

FIG. 8 illustrates a CPU 810, a memory 820, an address encryption unit830, a data encryption-decryption unit 840, a key storage 850, and anMMU (memory management unit) 860.

The CPU needs to store data in the memory 820. Moreover, the CPU 810needs to load data from the memory 820.

To transfer data from the CPU 810 to the memory 820 and from the memory820 to the 810, data buses are employed.

The CPU 810 uses plaintext data. However, data shall be stored in thememory 820 as ciphertext (encrypted data). Therefore, when the CPU 810wants to store (plaintext) data in the mentor), 820, the CPU 810 sendsthe plaintext data to the data encryption-decryption unit 840 via a databus. The data encryption-decryption unit 840 encrypts the plaintext datato obtain ciphertext data and stores the ciphertext data in the memory820. When the CPU 810 wants to load data from the memory 820, theencrypted data is loaded from the memory 820 and fed into the dataencryption-decryption unit 840 The data encryption unit 840 decrypts theciphertext data to obtain plaintext data and transmits the plaintextdata to the CPU 810.

For encrypting plaintext data and for decrypting ciphertext data, thedata encryption-decryption unit 840 may use a (cryptographic) key storedin a particular memory area, the key storage 850.

The CPU 810 may know a logical address of data being stored in thememory 820.

For storing data at an original logical address, the CPU 810 passes theoriginal logical address to the MMU 860. The MMU 860 may shift theoriginal logical address to obtain a shifted logical address and passesthe shifted logical address to the address encryption d u le 830. Theaddress encryption module 830 encrypts, by employing address encryption,the shifted address into a physical address. The physical address ispassed to the memory 820 via an address bus, so that the memory 820 isaware where the data is to be stored.

The address encryption unit 830 may an apparatus for encrypting an inputmemory address according to one of the above-described embodiments.

For loading data from an original logical address, the CPU 810 againpasses the original logical address to the MMU 860. The MMU 860 mayshift the original logical address to obtain a shifted logical addressand passes the shifted logical address to the address encryption module830. The address encryption module 830 encrypts, by employing addressencryption, the shifted logical address into a physical address. Thephysical address is passed to the memory 820 via an address bus, so thatthe memory 820 is aware where the data, which shall be loaded, islocated.

For address encryption, the address encryption unit 830 may use a(cryptographic) key stored in a particular memory area, the key storage850.

In particular, FIG. 8 illustrates an embodiment of an apparatus,comprising:

-   -   a CPU 810 for providing an original logical address,    -   an MMU 860 for generating a shifted logical address depending on        the original logical address.    -   an address encryption unit 830 for encrypting the shifted        logical address to obtain a physical address, the address        encryption unit 830 comprising an input interface for receiving        the shifted logical address, and further comprising an        encryption module for encrypting the shifted logical address        depending on a cryptographic key to obtain the physical address,        wherein the encryption module is configured to encrypt the        shifted logical address by applying a map mapping the shifted        logical address to the physical address, wherein the encryption        module is configured to apply the map by conducting a        multiplication and a module operation using the cryptographic        key and a divisor of the modulo operation, such that the map is        bijective,    -   a data encryption-decryption unit 840 for encrypting first        plaintext data to obtain first ciphertext data and for        decrypting second ciphertext data to obtain second plaintext        data,    -   a key storage 850 for storing the cryptographic key,    -   and a memory 820 being configured to either store the first        ciphertext data at the physical address, or to provide the        second ciphertext data being stored at the physical address to        the data encryption-decryption module.

Thus, a double protection is achieved, as can be seen in FIG. 9: Byencrypting the data, the plaintext data is substituted by ciphertextdata, so that an attacker cannot read the plaintext data. By encryptingthe original address to obtain an encrypted address, a transposition ofthe address is realized, and the data is not stored at the memorylocation indicated by the original address but is instead stored at theencrypted address. Thus, an attacker is not aware, where the data isstored, and moreover, data at subsequent logical addresses is stored atcompletely different physical locations in the memory, as addressencryption is employed.

Although some aspects have been described in the context of anapparatus, it is clear that these aspects also represent a descriptionof the corresponding method, where a block or device corresponds to amethod step or a feature of a method step. Analogously, aspectsdescribed in the context of a method step also represent a descriptionof a corresponding unit or item or feature of a corresponding apparatus.

The inventive decomposed signal can be stored on a digital storagemedium be transmitted on a transmission medium such as a wirelesstransmission medium or a wired transmission medium such as the Internet.

Depending on certain implementation requirements, embodiments ofembodiments can be implemented in hardware or in software. Theimplementation can be performed. using digital storage medium, forexample a floppy disk, a DVD, a CD, a ROM, a PROM, an EPROM, an EEPROMor a FLASH memory, having electronically readable control signals storedthereon, which cooperate (or are capable of cooperating) with aprogrammable computer system such that the respective method isperformed.

Some embodiments according to embodiments comprise a non-transitory datacarrier having electronically readable control signals, which arecapable of cooperating with a programmable computer system, such that meof the methods described herein is performed.

Generally, embodiments of the present invention can be implemented as acomputer program product with a program code, the program code beingoperative for performing one of the methods when the computer programproduct runs on a computer. The program code may for example be storedan a machine-readable carrier.

Other embodiments comprise, the computer program for performing one ofthe methods described herein, stored on a machine-readable carrier.

In other words, an embodiment of the inventive method is, therefore, acomputer program having a program code for performing one of the methodsdescribed herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a datacarrier (or a digital storage medium, or a computer-readable medium)comprising, recorded thereon, the computer program for performing one ofthe methods described herein.

A further embodiment of the inventive method is, therefore, a datastream or a sequence of signals representing the computer program forperforming one of the methods described herein. The data stream or thesequence of signals may for example be configured to be transferred viaa data communication connection, for example via the Internet.

A further embodiment comprises a processing means, for example acomputer, or a programmable logic device, configured to or adapted toperform one of the methods described herein.

A further embodiment comprises a computer having installed thereon thecomputer program for performing one of the methods described herein.

In some embodiments, a programmable logic device (for example a fieldprogrammable gate array) may be used to perform some or all of thefunctionalities of the methods described herein. In some embodiments, afield programmable gate array may cooperate with a microprocessor inorder to perform one of the methods described herein. Generally, themethods are performed by any hardware apparatus.

While this invention has been described in terms of several advantageousembodiments, there are alterations, permutations, and equivalents whichfall within the scope of this invention. It should also be noted thatthere are many alternative ways of implementing the methods andcompositions of the present invention. It is therefore intended that thefollowing appended claims be interpreted as including all suchalterations, permutations, and equivalents as fall within the truespirit and scope of the present invention.

The above described embodiments are merely illustrative for theprinciples of the present invention. It is understood that modificationsand variations of the arrangements and the details described herein willbe apparent to others skilled in the art. It is the intent, therefore,to be limited only by the scope of the impending patent claims and notby the specific details presented by way of description and explanationof the embodiments herein.

Although each claim only refers back to one single claim, the disclosurealso covers any conceivable combination of claims.

What is claimed is:
 1. An apparatus for encrypting an input memoryaddress to obtain an encrypted memory address, comprising: an inputinterface configured to receive the input memory address being anaddress of a memory, a segmentation module configured to segment theinput memory address into a plurality of input memory address segments,and an encryption module configured to encrypt each input memory addresssegment of the plurality of input memory address segments depending on arespective one of a plurality of cryptographic subkeys, wherein theencryption module is configured to encrypt said input memory addresssegment by applying a map mapping said input memory address segment toan encrypted memory address segment, said encrypted memory addresssegment being one of a plurality of encrypted memory address segments,wherein the encryption module is configured to apply the map byconducting a multiplication and a modulo operation using one of theplurality of cryptographic subkeys and one of a plurality of divisors,such that the map is bijective, wherein the encrypted memory addresssegments of the plurality of encrypted memory address segments togetherform the encrypted memory address.
 2. The apparatus of claim 1, whereineach of the plurality of input memory address segments indicates apolynomial of a first group of polynomials, wherein each of theplurality of encrypted memory address segments indicates a polynomial ofa second group of polynomials, wherein each of the plurality ofcryptographic subkeys indicates a third polynomial, and wherein each ofthe plurality of divisors indicates a fourth polynomial being anirreducible polynomial.
 3. The apparatus of claim 1, wherein theencryption module is configured to encrypt each of the input memoryaddress segments by applying said map mapping said input memory addresssegment to on of the plurality of encrypted memory address segments, byemploying the formulaa _(i) ′=a _(i) k _(i)(mod p _(i)), wherein i indicates an index of saidinput memory address segment, wherein a_(i) indicates said input memoryaddress segment, wherein a_(i)′ indicates said one of the plurality ofencrypted memory address segments, wherein k_(i) indicates one of theencryption subkeys, and wherein p_(i) indicates one of the divisors. 4.The apparatus of claim 3, wherein the apparatus is configurable toselect for each input memory address segment al of the input memoryaddress segments an identity key as the encryption key k_(i), such thata_(i) k_(i) (mod p_(i))=a_(i) (mod p_(i)).
 5. The apparatus of claim 3,wherein the apparatus is configurable to select for each input memoryaddress segment as of the input memory address segments a zero key asthe encryption key k_(i), such that a_(i) k_(i) (mod p_(i))=0.
 6. Theapparatus of claim 1, wherein the encryption module is configured toencrypt each of the input memory address segments by applying said mapmapping said input memory address segment to one of the plurality ofencrypted memory address segments, by employing the formulaa _(i) ′=a _(i) k _(i)(mod p _(i))+b _(i), wherein i indicates an indexof said input memory address segment, wherein a_(i) indicates said inputmemory address segment, wherein a_(i)′ indicates said one of theplurality of encrypted memory address segments, wherein k_(i) indicatesone of the encryption subkeys, wherein p_(i) indicates one of thedivisors, and wherein b_(i) indicates one of a plurality of auxiliarykeys.
 7. The apparatus of claim 6, wherein the apparatus is configurableto select for each input memory address segment ad of the input memoryaddress segments an identity key as the encryption key k_(i), such thata _(i) k _(i)(mod p _(i) 0+b _(i) =a _(i)(mod p _(i))+b _(i).
 8. Theapparatus of claim 6, wherein the apparatus is configurable to selectfor each input memory address segment as of the input memory addresssegments a zero key as the encryption key k_(i), such thata _(i) k _(i)(mod p _(i))+b _(i) =b _(i).
 9. The apparatus of claim 1,wherein the encryption module is configured to conduct themultiplication and the modulo operation further using one or more bitsof the input memory address other than bits of the input memory addresssegment being mapped.
 10. An apparatus comprising: a microprocessor forproviding an original logical address, an MMU for generating a shiftedlogical address depending on the original logical address, an addressencryption unit for encrypting the shifted logical address to obtain aphysical address, the address encryption unit comprising an inputinterface for receiving the shifted logical address, and furthercomprising an encryption module for encrypting the shifted logicaladdress depending on a cryptographic key to obtain the physical address,wherein the encryption module is configured to encrypt the shiftedlogical address by applying a map mapping the shifted logical address tothe physical address, wherein the encryption module is configured toapply the map by conducting a multiplication and a modulo operationusing the cryptographic key and a divisor of the modulo operation, suchthat the map is bijective, a data encryption-decryption unit forencrypting first plaintext data to obtain first ciphertext data and fordecrypting second ciphertext data to obtain second plaintext data, a keystorage for storing the cryptographic key, and a memory being configuredto either store the first ciphertext data at the physical address, or toprovide the second ciphertext data being stored at the physical addressto the data encryption-decryption module.
 11. A method for encrypting aninput memory address to obtain an encrypted memory address, comprising:receiving the input memory address being an address of a memory,segmenting the input memory address into a plurality of input memoryaddress segments, and encrypting each input memory address segment ofthe plurality of input memory address segments depending on a respectiveone of a plurality of cryptographic subkeys to obtain the encryptedmemory address, wherein encrypting said input memory address segmentcomprises applying a map mapping said input memory address segment to anencrypted memory address segment of a plurality of encrypted memoryaddress segments by conducting a multiplication and a modulo operationusing one of the plurality of cryptographic subkeys and one of aplurality of divisors, such that the map is bijective, wherein theencrypted memory address segments of the plurality of encrypted memoryaddress segments together form the encrypted memory address.
 12. Themethod of claim 11, wherein each of the plurality of input memoryaddress segments indicates a polynomial of a first group of polynomials,wherein each of the plurality of encrypted memory address segmentsindicates a polynomial of a second group of polynomials, wherein each ofthe plurality of cryptographic subkeys indicates a third polynomial, andwherein each of the plurality of divisors indicates a fourth polynomialbeing an irreducible polynomial.
 13. The method of claim 11, whereinconducting the multiplication and the modulo operation further uses oneor more bits of the input memory address other than bits of the inputaddress segment being mapped.
 14. A computer program for implementingthe method of claim 11, when being executed by a computer or signalprocessor.